There’s been a large amount of discussion surrounding the Korra release date, it’s changed several times (which is very common in media like this).
Bryan Konietzko just talked about the work and effort that goes into Korra, I think this about sums it up:
“We are only interested in putting out quality work, not doing it on the “fast and cheap” just so we can hurry up and get it out there.” – Bryan Konietzko (Co Creator)
Click Here To Read The Entire Article by Bryan
So Korra is getting the time and effort it deserves following ATLA, be patient for it, and definitely don’t get mad. Korra will come in good time 
Excellence like this can’t be rushed.
To second Bryan, Korra, and a Singing Fish "Don't Worry, Be Happy Now"
